Recording-2025-02-13T17_46_16.965Z

Introduction to the Motor System

• The motor system is responsible for impulses originating from the central nervous system and reaching the body.

• Two subdivisions:

  • Somatic Nervous System: Innervates skeletal muscles.

  • Autonomic Nervous System: Innervates smooth and cardiac muscles, typically under involuntary control.

Somatic Nervous System

• Regulators of skeletal muscle function.

• Important for voluntary movements and related to the next topic of skeletal muscles.

Anatomy Overview

• Impulses originate from the brain, influencing muscle movement.

• Cerebellum: Integrates sensory information related to equilibrium, balance, and proprioception.

• Sensory Receptors:

  • Muscle Spindles: Located within skeletal muscles, providing feedback on muscle length and rate of change.

  • Golgi Tendon Organs: Embedded in tendons, providing information on muscle tension.

Organization of Somatic Motor System

• Lower Motor Neurons:

  • Located in the ventral horn of the spinal cord or brainstem.

  • Travel to skeletal muscles through the ventral root of spinal nerves.

  • Function as a final common pathway (one neuron to one muscle).

  • Influenced by sensory feedback, which may have facilitatory or inhibitory effects.

Motor Pathway Circuits

1. Lower Motor Neurons:

   • Located in the brainstem/spinal cord.

   • Directly responsible for muscle contraction.

   • Evidence of commissural and ipsilateral tracts.

2. Upper Motor Neurons:

   • Input to lower motor neurons, playing key roles in voluntary movements.

   • Examples include direct and indirect motor pathways from the brain.

3. Basal Ganglia System:

   • Regulates initiation and control of motor responses based on sensory input and feedback.

   • Plays a significant role in forming correct motor responses.

   • Degeneration Example: Huntington's disease demonstrates how basal nuclei degeneration affects movement control.

Role of Cerebellum

• Acts like a ‘tattle tale’ to the primary motor cortex by comparing intended movements with actual movements.

• Functions under high complexity due to continuous sensory input and motor command integration.

Direct and Indirect Motor Pathways

• Direct Motor Pathways:

  • Deliver signals from the cerebral cortex to lower motor neurons, controlling voluntary movements.

• Indirect Motor Pathways:

  • Involved in reflexes and posture control.

  • Corticospinal Pathways: Includes lateral and anterior corticospinal tracts.

• Hyperdirect Pathway: Rapidly influences motor control independently of voluntary processes.

Basal Ganglia and Voluntary Movement

• Comprised of structures like the caudate nucleus, putamen, and globus pallidus, crucial for motor control.

• Involvement in voluntary movement selection and abnormal movement patterns in disorders like Huntington's disease.

Cerebellum's Motor Functions

• Coordinates voluntary muscle movements by processing incoming sensory information from various sources (muscles, joints, ears, eyes).

• Sends corrective signals to the motor cortex rather than directly influencing muscle contractions.

Cerebellar Input and Output

• Cerebellar pathways receive input from different sources to ensure precise motor output.

• Highlights the distinction between actual movements and intended movements via corrections sent to the primary motor cortex.

Conclusion

• The motor system encompasses a complex interaction between the central nervous system and muscles, with specific pathways and structures playing pivotal roles in coordinating voluntary and involuntary muscle movements.